Test Code MISC2MAYO7AC4 7AC4, Bile Acid Synthesis, Serum
Specimen Required
Patient Preparation:
1. Patient must be fasting for at least 12 hours; fasting morning specimen is preferred.
2. Patient should not be taking bile acid sequestrants or statins.
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 1 mL
Collection Instructions:
1. Centrifuge and aliquot 1 mL of serum into plastic vial.
2. Send specimen frozen.
Secondary ID
607699Useful For
Screening for bile acid malabsorption in patients with irritable bowel syndrome-diarrhea (IBS-D)
Method Name
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
Reporting Name
7AC4, Bile Acid Synthesis, SSpecimen Type
SerumSpecimen Minimum Volume
0.5 mL
Specimen Stability Information
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Serum | Frozen (preferred) | 90 days | |
Refrigerated | 72 hours | ||
Ambient | 24 hours |
Reject Due To
All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.Clinical Information
Bile acids are synthesized from cholesterol in the liver and released into the digestive tract where they function to emulsify dietary fats and facilitate lipid absorption in the small intestine. More than 95% of bile acids are then reabsorbed primarily by active uptake in the distal ileum, while less than 5% are excreted in stool. The synthesis of bile acids in the liver is regulated by a negative feedback mechanism from the bile acids reabsorbed from the intestine. 7 Alpha-hydroxy-4-cholesten-3-one (7aC4) is an intermediate in the biosynthesis pathway of cholesterol to bile acids. The concentration of 7aC4 in serum is a surrogate for the amount of bile acid synthesis in the liver. There is some diurnal variation in 7aC4 serum concentrations, so measurement should be performed on a fasting morning sample.
Patients with increased bile acid in their stool suffer from chronic diarrhea termed bile acid diarrhea (BAD). Approximately 10% to 33% of patients with irritable bowel syndrome with primarily diarrhea (IBS-D) have BAD. Identifying patients with BAD can be done by measuring total and fractionated bile acids in stool. The increased bile acids in feces can be caused by an inability to reabsorb bile acids in the terminal ileum (bile acid malabsorption: BAM). The loss of intestinal reabsorption leads to increase synthesis of bile acids in the liver. Recent studies have shown that serum concentrations of 7aC4 are elevated in patients with BAD and can be used as a surrogate to the timed fecal collection. Several intestinal diseases or functional abnormalities can lead to BAD. Identification of these patients can influence treatment decisions that could include the use of bile acid sequestrants.
Conversely, patients with IBS with predominately constipation (IBS-C) may have lower circulating 7aC4 as compared to healthy individuals.
Reference Values
≥18 years: 2.5-63.2 ng/mL
Reference values have not been established for patients who are <18 years of age.
Interpretation
In patients with irritable bowel syndrome-diarrhea (IBS-D), elevated 7alpha-hydroxy-4-cholesten-3-one (7aC4) is consistent with bile acid diarrhea (BAD). A result of 17.6 ng/mL or greater is 83% sensitive and 53% specific for BAD. In these cases, a confirmatory 48-hour fecal bile acid test could be considered. A result above 52.5 ng/mL is 40% sensitive and 85% specific for BAD.
Interpretation in patients with chronic diarrhea (bile acid malabsorption: BAM):
-------------------------------------------------17.6------------------------------------------52.5--------------------------
BAM unlikely Indeterminate BAM likely
(consider other (consider confirmatory (consider bile acid
conditions) fecal bile acids test or trial sequestrant therapy)
of bile acid sequestrant)
Method Description
7 Alpha-hydroxy-cholesten-3-one (7aC4) is extracted from the sample. After addition of a deuterium-labeled 7aC4 internal standard, 7aC4 is measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS).(Donato LJ, Lueke A, Kenyon SM, Meeusen JW, Camilleri M: Description of analytical method and clinical utility of measuring serum 7-alpha-hydroxy-4-cholesten-3-one (7aC4) by mass spectrometry. Clin Biochem. 2018;52:106-111)
Day(s) Performed
Wednesday
Report Available
2 to 9 daysPerforming Laboratory

Test Classification
This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
82542
LOINC Code Information
Test ID | Test Order Name | Order LOINC Value |
---|---|---|
7AC4 | 7AC4, Bile Acid Synthesis, S | 94866-1 |
Result ID | Test Result Name | Result LOINC Value |
---|---|---|
65504 | 7AC4, Bile Acid Synthesis, S | 94866-1 |
Forms
If not ordering electronically, complete, print, and send Gastroenterology and Hepatology Client Test Request (T728) with the specimen